KR100275488B1 - Multi quantum well structured passive optical waveguide integrated very high speed optical modulator, manufacturing method thereof and optical modulating method using the same - Google Patents

Abstract

PURPOSE: A very high speed optical modulator, a manufacturing method thereof and optical modulating method using the same are provided to prevent crystal defects and thus degradation of device through regrowth process by providing passive optical waveguide integrated optical modulator without regrowth process. CONSTITUTION: A very high speed optical modulator comprises a first clad layer on a semiconductor substrate, a multi quantum well structured optical absorption layer(11A) on a center portion of the first clad layer, a passive optical waveguide(11B) on the first clad layer and on opposite sides of the optical absorption layer, a second clad layer(13) on the optical absorption layer and passive optical waveguide, an insulating layer(14) on an interface of the optical absorption layer and passive optical waveguide, an electrode for applying voltage on the optical absorption layer and passive optical waveguide, and an anti-reflection layer adjacent to the first clad layer, passive optical waveguide and second clad layer. The optical absorption layer and passive optical waveguide are of same multi quantum well structured semiconductor layer.

Description

Ultra-fast optical modulator integrated with passive optical waveguides of multiple quantum well structures and its manufacturing method and optical modulation method using the same

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to the field of optical device manufacturing, and more particularly, to a high speed optical modulator integrated with a passive optical waveguide having a multi-quantum well structure, a method of manufacturing the same, and an optical modulation method using the same.

As the transmission speed and the transmission distance of the optical communication system increase, the light source requires higher performance in terms of modulation speed and modulation beam width. Since 1997, the long-distance transmission between stations is to use a transmission speed of more than 10Gbps, the direct modulation method of the semiconductor laser has a limitation in providing such a transmission rate. In order to solve this problem, a method of modulating a narrow line width semiconductor laser light into an transmission signal using an external optical modulator has been proposed. The external optical modulator has a structure using a change in refractive index and a method using a change in absorptivity. The dual field absorption type optical modulator has a high modulation speed of about 40 GHz to 60 GHz and can be designed with a structure having no polarization dependency and low operating voltage. Have.

The modulation rate of the ultrafast optical modulator is determined by the parasitic capacitance of the electrode and the capacitance of the modulator absorber layer. The parasitic capacitance of the electrode can be solved by forming a thick dielectric material under the electrode, such as polyimide, but in the design for reducing the capacity of the absorbing layer, the change of structure is necessary for the optical modulator such as extinction ratio and operating voltage. Because of its nature, an optimization design is required.

In general, the capacity of the optical modulator absorption layer is proportional to the length and width of the optical waveguide and inversely proportional to the thickness. Accordingly, a short modulator absorption layer waveguide of about 50 μm to 100 μm is required for ultra high speed operation, and FIG. 1 shows the structure of such a conventional ultra high speed optical modulator. However, when cutting a wafer into such a short length for a low capacitance modulator, cleaving itself is quite difficult and it is also impossible to secure the size of the electrode for wire bonding.

Accordingly, the entire length of the optical modulator is InGaAsP passive optical waveguide layer having a large band gap by the epitaxial regrowth method as shown in FIG. 2 for low capacitance while maintaining a convenient length for packaging. 6) has been proposed to increase the overall length of the optical modulator by integrating. However, such a method of manufacturing an optical modulator through epitaxy regrowth requires an additional epitaxy process, and has disadvantages such as a problem of deterioration of reliability of a device due to crystal defects in terms of optical coupling formed by regrowth.

The present invention devised to solve the above problems provides a multi-quantum well structure that can prevent the deterioration of the reliability of the device due to crystal defects according to the regrowth process by providing an optical modulator integrated with a passive optical waveguide without a regrowth process. It is an object of the present invention to provide a highly integrated ultra-fast optical modulator having a passive optical waveguide having a light, a method of manufacturing the same, and an optical modulation method using the same.

1 is a schematic diagram of a short ultrafast optical modulator of a conventional light absorbing layer;

2 is a schematic diagram of a conventional ultrafast optical modulator in which a passive optical waveguide is integrated by an epitaxy regrowth method to increase the length of the entire optical modulator.

Figure 3a is a cross-sectional view showing an absorption layer and a cladding layer of a multi-quantum well structure

FIG. 3B is a graph showing changes in electric field according to voltages applied to the light modulator absorption layer (I) region and the undoped clad layer (II) region of FIG. 3A.

4 is a graph showing the change in absorption coefficient spectrum of a multi-quantum well structure according to applied voltage

Figure 5a is a perspective view schematically showing an optical modulator according to an embodiment of the present invention

FIG. 5B is a cross sectional view along line A-A in FIG. 5A

6A to 6C are cross-sectional views of an optical modulator manufacturing process according to an embodiment of the present invention.

* Description of reference numerals for the main parts of the drawings

1, Ⅰ, 11A: light modulator absorption layer

2, 12: n-type InP cladding layer

3, 13: p-type InP cladding layer

4: Ohmic contact metal layer of light modulator

5, 15: antireflective thin film

6, 11B: passive optical waveguide layer

II: Undoped InP Clad Layer

a: electric field applied to the multi-quantum well structure when forward 1V voltage is applied

b: electric field applied to multiple quantum well structures at built-in voltage

c: electric field applied to the multi-quantum well structure when reverse 2V voltage is applied

α: absorption coefficient spectrum of multiple quantum well structure when forward 1V voltage is applied

β: Absorption coefficient spectrum of multiple quantum well structure at built-in voltage

γ: absorption coefficient spectrum of multi-quantum well structure when reverse 2V voltage is applied

10A: electrode for applying reverse voltage to modulator section

10B: electrode for applying forward voltage to part of passive optical waveguide

14: insulation layer

The present invention for achieving the above object is a first cladding layer located on a semiconductor substrate; A light absorbing layer having a multi-quantum well structure positioned at a central portion on the first clad layer; A passive optical waveguide layer having a multi-quantum well structure positioned above the first cladding layer and on both ends of the light absorbing layer; A second clad layer disposed on the light absorption layer and the passive optical waveguide layer; An insulating layer positioned on a boundary between the light absorption layer and the passive optical waveguide layer in the second cladding layer; An electrode for independently applying a voltage on the light absorption layer and the passive optical waveguide layer; And an antireflection film in contact with both side surfaces of the first cladding layer, the passive optical waveguide layer, and the second cladding layer, to provide an optical modulator integrated with a passive optical waveguide having a multi-quantum well structure.

In addition, the present invention for achieving the above object is applied to the light absorbing layer of the multi-quantum well structure located in the center between the first cladding layer and the second cladding layer on the semiconductor substrate through the second cladding layer, An optical modulator is disposed between the first cladding layer and the second cladding layer, by applying a forward voltage to each of the passive optical waveguide layers having a multi-quantum well structure connected to both ends of the light absorbing layer through the second cladding layer. Provided is an optical modulation method for modulating light incident on an input surface into on-off and outputting the light to an optical output surface.

In addition, the present invention for achieving the above object is a first step of forming a first cladding layer on a semiconductor substrate; A second step of forming a semiconductor layer having a multi-quantum well structure that forms a light absorption region and a passive optical waveguide region for each region on the first clad layer; A third step of forming a second cladding layer on the semiconductor layer of the multi quantum well structure; Forming an insulating layer in the second clad layer to divide the semiconductor layer of the multi-quantum well structure into a light absorption region and a passive optical waveguide region adjacent to both ends of the light absorption region; And a fifth step of forming an electrode corresponding to each of the light absorbing region and the passive optical waveguide region on the second clad layer, wherein the passive optical waveguide of the multi-quantum well structure is integrated. .

DETAILED DESCRIPTION Hereinafter, exemplary embodiments of the present invention will be described with reference to the accompanying drawings so that those skilled in the art may easily implement the technical idea of the present invention.

In the semiconductor optical modulator, a method of applying an electric field to an absorbing layer without current flow is generally a method of applying a reverse voltage to a p-type (hole) -intrinsic-n-type (electron) (pin) semiconductor junction. . In this case, an electric field of about 30 kV / cm (1 V / 0.3 μm) is formed by its built-in voltage even without an externally applied voltage.

FIG. 3A is a cross-sectional view showing an absorbing layer and a cladding layer having a multi-quantum well structure, showing an n-type cladding layer 2, an absorbing layer I region, and a p-type cladding layer 3, and FIG. I) Schematic representation of the distribution of each electric field for the absence of forward, reverse and external applied voltages in the region and undoped clad region (II), where a denotes a multiple quantum well when a forward 1V voltage is applied. The electric field applied to the structure, b is the electric field applied to the multi quantum well structure at the built-in voltage, c is the electric field applied to the multi quantum well structure when a reverse 2V voltage is applied.

As shown in FIG. 3B, when the forward 1V voltage is applied, the electric field a applied to the multi-quantum well structure is in a state where the electric field is close to 0 kV / cm, that is, there is little electric field, and there is no external applied voltage. The electric field (b) applied to the multi-quantum well structure at the built-in voltage generates an electric field of about 30 kV / cm by the built-in voltage, and when the reverse 2V voltage is applied, the electric field (c) applied to the multi-quantum well structure is 90 An electric field of about kV / cm is generated.

The absorption coefficient of the optical modulator absorption layer changes according to the size of the electric field due to the quantum confinement stark effect. 4 is a graph showing the change of absorption coefficient of a multi-quantum well structure according to the light wavelength, where α is an absorption coefficient spectrum of a multi-quantum well structure when a forward 1V voltage is applied, and β is an absorption coefficient of a multi-quantum well structure at a built-in voltage. The spectrum, γ, represents the absorption coefficient spectrum of the multi-quantum well structure when the reverse 2V voltage is applied, respectively.

As can be seen from Fig. 4, when there is no externally applied voltage at 1.55 占 퐉 wavelength used in long-distance optical communication, that is, when the built-in voltage and the reverse 2V voltage are applied, the change in absorption coefficient is large and thereby the transmitted light is modulated. . That is, when there is no external voltage at 1.55 ㎛ wavelength, the absorption coefficient is relatively small and light passes through the optical modulator absorption layer (around 50%), and when the reverse external voltage is applied, the absorption coefficient increases and the incident light is mostly It is absorbed by the optical modulator absorbing layer and cannot pass through the optical modulator.

Even when there is no externally applied voltage, an electric field is applied to the absorbing layer by the built-in voltage as described above, and a considerable amount of light absorption occurs due to the quantum binding stark effect. At this time, if the electric field generated by the built-in voltage is removed by applying the forward voltage, the increase in the absorption coefficient due to the built-in voltage is prevented, so that most of the light is transmitted without being absorbed by the absorbing layer. Therefore, when a forward voltage of about 1V is applied to a portion of a passive optical waveguide that requires low loss, the multi-quantum well structure layer of this portion serves as an optical waveguide with almost no absorption loss.

FIG. 5A is a schematic perspective view of an ultrafast optical modulator integrated with a passive optical waveguide of a multi-quantum well structure according to an embodiment of the present invention, and FIG. 5B is a cross-sectional view taken along line AA of FIG. 5A, and FIG. Is an electrode for applying reverse voltage to the modulator portion, 10B is an electrode for applying a forward voltage to the passive optical waveguide portion, 11A is an optical modulator absorbing layer of a multi-quantum well structure, 11B is a passive optical waveguide layer of a multi-quantum well structure, and 12 is An n-type cladding layer, 13 is a p-type cladding layer, 14 is an insulating layer, and 15 is an antireflection thin film, respectively.

The optical modulator absorption layer 11A and the passive optical waveguide layer 11B both have a multi-quantum well structure, and the optical modulator absorption layer 11A is located at the center of the optical modulator and has a length of 50 μm to 100 μm. The passive optical waveguide layer 11B is located on both sides of the optical modulator absorbing layer 11A and has a length of 100 μm to 300 μm such that the total length of the optical modulator is about 250 μm to 700 μm. This allows obtaining a length sufficient for bonding the antireflective thin film 15 and bonding for the package.

The modulator absorbing layer 11A and the passive optical waveguide layer 11B are ion implanted or etched to apply a reverse voltage to the modulator absorbing layer 11A and a forward voltage to the passive optical waveguide layer 11B. It is electrically separated through the same process. 5B shows an example in which the insulating layer 14 is formed between the modulator absorbing layer 11A and the passive optical waveguide layer 11B through ion implantation.

6A through 6C are cross-sectional views illustrating a manufacturing process of an ultra-high speed optical modulator integrated with an optical waveguide having a multi-quantum well structure according to an embodiment of the present invention.

First, as shown in FIG. 6A, an n-type cladding layer 12 is formed on an InP substrate (not shown), and a bandgap energy having an optical wavelength of 1.5 μm is formed on the n-type cladding layer 12. A semiconductor layer having a quantum well structure is formed. The semiconductor layer of the multi-quantum well structure is divided into an optical modulator absorption layer 11A and a passive optical waveguide layer 11B. Subsequently, the p-type cladding layer 13 is formed on the semiconductor layer having the multi-quantum well structure.

Next, as illustrated in FIG. 6B, hydrogen (H) or boron (B) is ion-implanted into the p-type cladding layer 13 to form a boundary between the optical modulator absorption layer 11A and the passive optical waveguide layer 11B. The insulating layer 14 is formed. The insulating layer 14 may be formed by etching the p-type cladding layer 13.

Next, as shown in Fig. 6C, p-type electrodes 10A and 10B of Ti / Pt / Au are formed on the optical modulator absorption layer 11A and the passive optical waveguide layer 11B, respectively.

Subsequently, polyimide is applied to the portion where the wire bonding pad is to be formed to reduce parasitic capacitance, plated Au on the bonding pad portion, lapping of the wafer for separation of the device and n-type of Cr / Au. After depositing an electrode and cleaving the wafer to a predetermined length of about 500 μm, an antireflective thin film is deposited on both sides to form an optical modulator.

A forward voltage of about 1 V is applied to the passive optical waveguides on both sides of the optical modulator absorbing layer and the voltage incident to the optical modulator input surface is turned on and off by applying a voltage of 0 V to -2 V to the optical modulator absorbing layer electrode. on-off) to output to the optical output surface. Note that the optical modulator according to the present invention is symmetric and there is no distinction between the input and output directions.

The present invention described above is not limited to the above-described embodiments and the accompanying drawings, and various substitutions, modifications, and changes can be made in the art without departing from the technical spirit of the present invention. It will be apparent to those of ordinary knowledge.

The present invention made as described above provides an optical modulator integrated with a passive optical waveguide having a multi-quantum well structure. As a result, an optical modulator having an easy antireflection thin film deposition process and a length sufficient to be able to be packaged can be formed without a regrowth process, thereby preventing deterioration of the reliability of the device due to crystal defects.

In addition, by forming an electrode in the passive optical waveguide portion having the multi-quantum well structure of the modulator according to the present invention and applying a constant voltage of about 1V in the forward direction, it is possible to remove the built-in electric field with a simple operation and to inject a carrier. Due to the optical gain generated, the absorption coefficient itself is also reduced, which can further reduce the loss of the passive optical waveguide layer.

In addition, since the optical modulator integrated with the passive optical waveguide of the multi-quantum well structure according to the present invention has a short absorption layer, the area of the optical modulator acting as a capacitance is small, and the capacitance of the bonding pad is reduced by using polyimide. Because of the reduction, ultra-fast modulation up to 40 GHz is possible.

Claims (14)

In the optical modulator, A first clad layer positioned on the semiconductor substrate; A light absorbing layer having a multi-quantum well structure positioned at a central portion on the first clad layer; A passive optical waveguide layer having a multi-quantum well structure positioned above the first cladding layer and on both ends of the light absorbing layer; A second clad layer disposed on the light absorption layer and the passive optical waveguide layer; An insulating layer positioned on a boundary between the light absorption layer and the passive optical waveguide layer in the second cladding layer; An electrode for independently applying a voltage on the light absorption layer and the passive optical waveguide layer; And And an antireflection film in contact with both sides of the first cladding layer, the passive optical waveguide layer, and the second cladding layer. The method of claim 1, And the light absorbing layer and the passive optical waveguide layer comprise a semiconductor layer having the same multiple quantum well structure. The method according to claim 1 or 2, And the electrodes are electrodes formed on the second cladding layer, respectively. The method of claim 3, wherein And the semiconductor layer of the multi quantum well structure has a bandgap energy corresponding to an optical wavelength of 1.5 μm. The method of claim 4, wherein And the first cladding layer is n-type, and the second cladding layer is p-type. The method of claim 5, The optical modulator integrated with the passive optical waveguide of the multi-quantum well structure, characterized in that the length of the light absorption layer is 50 ㎛ to 100 ㎛. The method of claim 6, The optical optical waveguide integrated with the passive optical waveguide of the multi-quantum well structure, characterized in that the length of the passive optical waveguide is 100 ㎛ to 300 ㎛. In the light modulation method, Applying a reverse voltage through the second clad layer to a light absorbing layer having a multi-quantum well structure positioned at the center between the first clad layer and the second clad layer on the semiconductor substrate; Located between the first cladding layer and the second cladding layer, by applying a forward voltage through the second cladding layer to each of the passive optical waveguide layer of the multi-quantum well structure connected to both ends of the light absorbing layer, An optical modulation method for modulating light incident on an optical modulator input surface into an on-off output to an optical output surface. The method of claim 8, The magnitude of the reverse voltage applied to the light absorbing layer does not exceed 2V. The method according to claim 8 or 9, And a magnitude of forward voltage applied to the passive optical waveguide layer is 1V. In the optical modulator manufacturing method, Forming a first cladding layer on the semiconductor substrate; A second step of forming a semiconductor layer having a multi-quantum well structure that forms a light absorption region and a passive optical waveguide region for each region on the first clad layer; A third step of forming a second cladding layer on the semiconductor layer of the multi quantum well structure; Forming an insulating layer in the second clad layer to divide the semiconductor layer of the multi-quantum well structure into a light absorption region and a passive optical waveguide region adjacent to both ends of the light absorption region; And And a fifth step of forming an electrode corresponding to each of the light absorbing region and the passive optical waveguide region on the second cladding layer. The method of claim 11, In the fourth step, A method for manufacturing an optical modulator integrated with a passive optical waveguide having a multi-quantum well structure, wherein the insulating layer is formed by implanting hydrogen or boron ions into the second clad layer. The method of claim 12, In the fifth step, And a p-type electrode of Ti / Pt / Au, wherein the passive optical waveguide of the multi-quantum well structure is integrated. The method of claim 13, After the fifth step, Applying a polyimide to a portion where a wire bonding pad is to be formed; A seventh step of plating Au on the wire bonding pad portion; And An eighth step of forming an n-type electrode of Cr / Au; And And a ninth step of forming an antireflective thin film on both surfaces of the first clad layer, the semiconductor layer of the multi-quantum well structure, and the second clad layer, wherein the passive optical waveguide of the multi-quantum well structure is integrated. Modulator manufacturing method.